But despite all the grief they cause, turns out there’s one major benefit to having them around: happiness.

According to researchers from De Montfont and Ulster Universities in the UK, having a sister makes you optimistic about life. For their study, they asked 571 people between the ages of 17 and 25 to fill out a questionnaire about their mental health.

The takeaway? The participants who grew up with sisters were way more content than those who didn't.